Growth hormone (GH) is essential for linear growth in man and other mammalian species. In order to understand the mechanisms controlling the production of this hormone, it is important to obtain information about the GH gene and the regulation of its expression. To facilitate the achievement of these goals, we have isolated and studied the structure of the rat (r) and human (h) GH genes and have used DNA containing rGH gene sequences to examine the expression of this gene in cultured pituitary cells and in the intact pituitary gland with particular emphasis on the mechanisms by which thyroid and glucocorticoid hormones affect GH gene expression. In the proposed studies, we plan to investigate in greater detail the expression of the rGH and hGH genes. To achieve these ends, we plan to use cultured rat pituitary tumor cells (GC, GH3 and GH4 sublines) and the intact pituitary gland of rats to examine the individual rGH mRNA precursors and byproducts and their regulation by hormones, the internal and normal promoters associated with the gene, the regulation and functional significance of two different mRNA forms that arise from the rGH gene, and the mechanisms by which hormones affect the synthesis and stability of rGH gene transcripts. The genomic structure relevant to the expression of the rGH gene in these cells will be investigated by examining the structure and expression of DNA sequences from regions flanking the gene. The features of the gene necessary for its ability to be regulated by thyroid hormones will be delineated by transferring the cloned rGH and hGH genes to a variety of cell types and the mechanism by which thyroid hormone acts will be studied with the use of hybrid gene constructions, gene deletions and a variety of vectors. Finally, the expression of the rGH and hGH genes will be examined by transcribing them in cell-free conditions with the aim towards a defined reconstitution of hormone action. The studies should provide primary information regarding the regulated expression of the growth hormone genes (and by inference about other genes) and about the mechanisms of thyroid and glucocorticoid hormone action.